You can invest a maximum of 31 books in your geologist. All skills have three levels excepts for the highest three (Lucky Find, Natural Born Digger, Nature's Gift), those only have one. Since the three highest skills require 30 books invested in the levels below, you can only choose one of these
Type: Manuscript
- Hidden Stone Stash
- Natural Copper Vein
- Two Marble in One *
- Quality Copper Mineshafts
- Natural Stone Vein
Type: Tome
- Natural Marble Vein
- Copper Mining Surplus
- Two Iron in One *
- Quality Coal Mineshafts
- Tendentious Geologist
- Gold Mining Surplus
Type: Codex
- Hidden Coal Stash
- Iron Mining Surplus
- Natural Gold Vein
- Two Coal in One *
- Quality Gold Mineshafts
- Ore Collector
- Lucky Find
- Natural Born Digger
- Nature's Gift
* The bonus deposit will NOT benefit from other skills that can upgrade these kind of deposits